Q: In the Zinc Chloride lab, students determine the empirical formula of zinc chloride by reacting zinc metal with hydrochloric acid. If a student starts with 1.73 g of Zn and obtains 2.95 g of ZnCl₂, what is the mass of chlorine in the product?

$$2.95 \text{ g} - 1.73 \text{ g} = 1.22 \text{ g}$$

Question 1

In the Zinc Chloride lab, students determine the empirical formula of zinc chloride by reacting zinc metal with hydrochloric acid. If a student starts with 1.73 g of Zn and obtains 2.95 g of ZnCl₂, what is the mass of chlorine in the product?

Accepted Answer

$$2.95 	ext{ g} - 1.73 	ext{ g} = 1.22 	ext{ g}$$

Question 2

Which of the following best describes the difference between a molecular formula and an empirical formula?

Accepted Answer

The molecular formula shows the actual number of atoms of each element in a molecule, while the empirical formula shows the simplest whole-number ratio of the elements.

Question 3

A student calculates the mole ratio of Cl to Zn in their product as $$2.11. $$What is the empirical formula of the compound they produced?

Accepted Answer

$$\mathrm{ZnCl}_2$$

Question 4

If a student’s calculated Cl mole ratio is much higher than expected, which experimental error is most likely responsible?

Accepted Answer

Some zinc did not react, so the mass of ZnCl₂ is lower than it should be.

Question 5

Given the following data: $$1.73 	ext{ g} Zn $$and $$1.22 	ext{ g} Cl$$, calculate the number of moles of Zn and Cl. ($$M_{Zn} = 65.38 	ext{ g/mol}$$, $$M_{Cl} = 35.45 	ext{ g/mol})$$

Accepted Answer

Zn: $$\frac{1.73}{65.38} = 0.0264$$ mol; Cl: $$\frac{1.22}{35.45} = 0.0344$$ mol

Question 6

After calculating moles of Zn and Cl, a student finds $$0.0264$$ mol Zn and $$0.0555$$ mol Cl. What is the simplest whole-number ratio of Cl to Zn?

Accepted Answer

$$\frac{0.0555}{0.0264} = 2.10$$

Question 7

Why is it important to use the mass of the empty beaker in the zinc chloride lab?

Accepted Answer

To accurately determine the mass of zinc and zinc chloride by subtracting the beaker’s mass from the total mass.

Question 8

If a student forgets to remove the lid from the beaker during heating, what error might occur in their results?

Accepted Answer

Gas produced (H₂) may not escape, leading to inaccurate mass measurements.

Question 9

Which of the following is the correct balanced chemical equation for the reaction between zinc and hydrochloric acid?

Accepted Answer

$$\mathrm{Zn} + 2\mathrm{HCl} \rightarrow \mathrm{ZnCl}_2 + \mathrm{H}_2$$

Question 10

A student’s data shows a yellowish tint to the liquid after the reaction. What is the most likely explanation?

Accepted Answer

Impurities or side reactions occurred, possibly due to incomplete reaction or contamination.

Question 11

If a student adds excess hydrochloric acid to the reaction, what effect does this have on the empirical formula calculation?

Accepted Answer

It does not affect the empirical formula as long as all zinc reacts and the product is isolated correctly.

Question 12

Which of the following is NOT a valid reason for a student’s calculated Cl mole ratio being higher than expected?

Accepted Answer

All zinc reacted completely and the product was isolated correctly.

Question 13

If the empirical formula of a compound is $$\mathrm{CH}_2\mathrm{O}$$ and its molar mass is $$180 	ext{ g/mol}$$, what is its molecular formula?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$$

Question 14

A student finds the mole ratio of Cl to Zn to be $$2.5. $$What empirical formula should they report?

Accepted Answer

$$\mathrm{ZnCl}_2 ($$rounded to nearest whole number)

Question 15

Why do chemists use empirical formulas instead of molecular formulas when analyzing unknown compounds?

Accepted Answer

Empirical formulas provide the simplest ratio of elements, which is useful for identifying unknown substances.

Question 16

During the zinc chloride lab, why is it important to heat the beaker until all liquid is gone?

Accepted Answer

To ensure all water is evaporated, leaving only solid zinc chloride for accurate mass measurement.

Question 17

If a student’s final mass of zinc chloride is greater than the theoretical yield, what is the most likely cause?

Accepted Answer

The product contains water or other impurities.

Question 18

Which calculation is necessary to determine the empirical formula from experimental data in the zinc chloride lab?

Accepted Answer

Convert masses of Zn and Cl to moles, then find the simplest whole-number ratio.

Zinc Chloride Lab Notes

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